Explosive charges are regularly used in the oil industry to perforate the metal casing across the reservoirs of oil and gas wells when the well is put into production. Explosives are used because they provide a concentrated energy source which is generally easy to handle.
Currently explosives used in boreholes are detonated by electrical, hydraulic or mechanical means. In electrically detonated systems, the signal and power for detonation are sent by wire to an electrically triggered detonator. It is thereby possible to remotely detonate the explosion. The wire together with the detonator, and possibly a plurality of detonators, form what is known as a firing circuit. The detonation of the devices is achieved by sending a sufficient amount of electrical power along the firing circuit and this is known as firing.
Such electrically detonated systems are susceptible to stray currents and stray radiation commonly referred to as electromagnetic interference and radio frequency interference (EMI/RFI) which can cause premature firing, or failure of the transmission of the signal. It is possible to remotely monitor the condition of the firing circuit before firing by using a test signal of a different magnitude. However this carries a risk that the test signal may in fact cause firing because the difference in magnitude between the detonation and test signals is not sufficiently great. This problem is exacerbated by the susceptibility to electromagnetic and radio frequency interference mentioned above. At present the risks are reduced by shutting down radios and equipment which are the source of stray electrical signals when explosives are in use but this is an expensive exercise on a busy oil platform.
Mechanically and hydraulically detonated systems use a remote mechanical or hydraulic link to a percussion detonator. There are no adverse effects from EMI or RFI but there are limits to the economical distances for the remote detonation. It also generally not possible to test the firing device without at the same time running the risk of detonating the explosive device.
In many of these detonation systems it is necessary to use a primary explosive in order to provide satisfactory detonation of the main, secondary explosive. These primary explosives provide additional handling problems and are characterized by an increased susceptibility to shock and fire.
In addition, with all the above existing detonation systems, there is a constant compromise between the reliability which increases with the ease with which the explosive can be detonated and the operational safety which decreases with the ease with which the explosive can be detonated.